Electric fuse



May 19, 1953 J, E, coi( 2,639,350

ELECTRIC FUSE Filed July 30, `95 :s Sheets-Sheet I l I l I Inventor Attorney J. E. COX

ELECTRIC FUSE May 19, 1953 3 Sheets-Sheet 2 Filed July 30,* 1951 J. E. COX

ELECTRIC FUSE May 19, 1953 Filed July 30, 1951 3 Sheets-Sheet 3 m\m nm mm mm V. m r m A wwi E mm L ;a

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Patented May 19, 1953 ELECTRIC FU SE John Edward Cox, Westlands, Newcastle, England Application July 30, 1951, Serial No. %9,289 In Great Britain August 11, 1950 13 Claims. (Cl. 200-120) This invention relates to electric fuses and in particular, to 'fuses in which one or more fusible conductors is enclosed in a tubular casing of insulating material closed at one or both ends by sealing caps. i. such fuses are often known as cartridge fuses and liquid fuses, and the tubular casing may be made of material such as porcelain glass, synthetic resin and so forth. It has been the usual practice to close the ends of the tubular bodies of such cartridge fuses by securing end 'caps into position by cementing them to the casing, pressing them, spinning them or providing a thin coating of metal over the end cap and body of the casing.

The objects of the present invention are .to provide a form of cartridge fuse in which the ends are sealed by a simple and cheap process and are effectively rendered gas-tight, water-tig'ht r and oil-tight at the sealed joints and, if desired' to make provision for indicators of the condition 1 of the fuse'jand to support the insulating core within the ca'sing in a simple and reliable fashion,

ii' such a core is employed. j According-,to the present invention, the sealed joint between the end cap and the tubular body of such an enclosed fuse is formed by one or more sealing rings' of yieldable material at each end',

`which rings 'are deformed under compression when the terminal caps are forced over the body' `of the casing. It is most convenient to provide 'grooves in the outer wall of the tubular casin'g; 'to house the scaling rings which are compress'ed when the smooth inner surface of the cap engages them,' but it is possible to make a` similar 'joint by means of grooves in the inner wall of the cap to receive yieldable rings, in which case the outer wall of'the tubular casing is smooth. such -rings may be of rubber or relatively soft thermo-V plastic synthetic resin or other yieldable pack-` ing material; i'.

The end'caps may also be adapted to aflord'a support for'a hollow star core of insulating material when such is employed, and then the iusi'b'le -conductor is supported on the core and the casing cylindricalwall of the casing and a re-entrant central portion of the end cap. In such a case the spigot supporting the star core may also serve the purpose of a housing for an indicator of the spring compressed plunger type or the explos-ive capsule type. Such an indicator usually has ;a

pointed plunger rod which indicates that the fuse has been blown when the rod protrudes. In normal use the rod may be enclosed within the end cap which has a thin wall at its centre portion which may be pierced by the pin of the indicator rod and then retains the latter in its outer indicating position. Yet again the star core may have the outwardly extending sleeve-shaped terminals at each end to which the fusible conductor is connected, and this terminal may engage over and make electrical connection with an inwardly projecting spigot on the respective end cap.

In order that the invention maybe clearly understood and readily carried into effect, some examples of Cartridge fuses constructed in'accordance with the present invention will now be more fully described with reference to the accompanyng drawings, in which: i

Figure 1 is a central axial section of a preferred form of the cartridge fuse;

Figure 2 is a cross-section on the line II-II;

Flgure 3 is an elevation of the body of the fuse shown in Figure 1 at one end and asection of the end cap in process of being forced on to the tubular casing; e

Figure 4 is an axial section of a modified for of Construction;

Figure 5 is an axial section of one end of yet another form;

Figure 6 is an elevation of one form showing the end cap with a mounting bracket and terminal securing it; while Figures 7 and 8 are respectively axial sections of two further modified forms of fuses in accordance with the invention. e

Referring first to Figures 1 to 3 which show a preferred form of high tension fuse, the tubular casing l consists of a cylindrical tube of glass moulded with two annular grooves 2 at either end, such grooves being of semi-circular section. Each of these grooves houses a rubber ring 3 which stands up from the casing I before the end cap is put into position, as shown in Figure 3. At each end a sheet metal end cap 4 is pressed over the tubular casing to compress and deform the rings 3, as indicated in Figure 1, and in order to avoid damage to the rings 3 or to force them out of their grooves 2, each endcap 4 has its mouth flared somewhat at 5. In this way the rings 3 are spread and form a gas and liquid-tight joint at each end of the casing I. As shown in the drawing, each sealing ring is of sufficient Volume, when compressed, to fill completely the annular groove in which it is located and there is sufiicient additional material to fill a substantial part of the annular space between the cap and the casing. The spreading of the scaling material into the spigo't 25 of the end caps 4.

support this in position there is at either end ari inner sheet metal cap 8 which fits resilientlw over a re-entrant part 9 of the end cap 4. The

inner cap 8 is also formed with a tubularspigot ID on which the star core 6 is supported. For' hand terminal 25 pushed over the spigot 26. The

tube casing I and the star core 6 are then filled withpowder as before and the inner cap 4 with the Washer 22 and the outer cap 24 at the right hand end pushed on. The housing 21 for the that purpose, at either end a yielding plug or and the spigot ID makes a good fit within'the plug ll.

A helix of silver wir" [2 bridging the ribs 1 is ,carriedon the outside of 'the 'core 5 :and is .spot welded at its-ende to the'inner caps 8 which are *conveniently-of coppenso thatthissilver conducr tor electrically connected between 'the end 'caps- 4." The inner cap 'a-at the right `hand end also serves-*as 'the housing .for an indieator 1-3 *of 'the' explosive capsule' `type which .makes 'a slidingfit within-:the spigot w. In'the example shown, the indicator -plunger na :has `a radialrod l.4-:-pressed outwards by a light spring :not shown, to uengage the' innerwall of :the spigot w so as tomake -electrical contact between the indicator plunger !3 and the spigot o of the cap .8-. The indicator has' a forwardly pointed red" !5 en- -closed `withinrthe end cap d'which has thin wall 16 at its' central part which 'can be 'pierced bythe poi-nted `'red i 5 when'the fuse is blown; and which thengrips the rod l5 'and retains it in the' in'- dicating position. The Iindicator' ta is exploded by a subsidiaryfusible conductor consisting of a ccil of tungsten wire 11.2 This wire at' the'left "hand 'end is'secured 'to 'a Copper -bridge'piece' 18 weldedat its ends to the inner 'cap !0,and at its other ,end'the' tungsten wire l' 'is :connected to theinner end 'of' the indicator i' so :as to'explode the capsule in the latter when the tungsten -wir i 'I fuses. There isa packingring or'washer IS of asbestos tted between the' inner wall of the casing I and the inner cap Rat-the lefthand end.

' In assembly the l-fuse, the right hand end cap 4 is forced -on to the end of the glass tube I in the manner already indicated. Then the star core `(i which has previously 'been fitted with the endcaps 8 and *plugs i I, the' indicator !3, `the Washer 2l and the silverconductor 4'2 .and tungsten conductor l'l ispushed in from 'the left 'until the Washer 2! :beds against the' inturned part 9 of .the right hand outer cap '4. Then .while :thexcore 8 is held central, the' space within the core and the enter space about the core is; packed with the marble powder 20; the washer= !9 is inserted and finally, the left hand end cap 4 is forced on into position.

In .Figure 4, the casing i is similar shownin Figure 1, with the sealing rings 3 compressed by the end caps 4.' In this case, however, 'at `either end a packing Washer 22 is compressed between the fiat end and the casing and ,the flat inner wall of the cap 4. A further asher 23 is placed outside the cap 4 and a plain end cap 24 pi'es'sed on to' the cap 4 to compress the washer '23.

In this'case also, the star core E has ribs 'I and at either end, has a sleeve-like terminal 25 cemented 'on to it as shown at 42 and the silver r fusible conductor !2 is spot welded to the terminals 25. The terminals* 25 are 'arranged to fit over and make connection with the inturned The 'assembly of the fuse is carried' 'out much to that indicator of the spring-pressed or explosive capsule type has its. outer end 28 of enlarged diamater andits'cylindrical wall slit, as shown at 29, so as to grip internally the right hand spigot 26 and to hold the housing in position. The indicator, however, is n'ot shown in Figure 4.

InFigure `5, the Construction is generally `as at the right hand end of Figure 1, the end-cap@ supporting'an inner cap 3 which enters a plug H forced into the bore of the star core 6-. 'The ;spigot li) of the inner cap 8 forms the housing for indicator 13 which is'of the explosivecapsule type. -Thisplunger is ormed 'with a numbertof thin .collars 30 `leaving grooves :between them which are intended-to be engaged by a pair of springy out-turned arms 39. which serve-as `retaining `pawls-'when fuse is blown and the-indicator` 13 is :forced `into its outer position. The arms 39 extend-inwardly .from a :ring ;heldlbetween the flat surface of the inner cap e anda acking ring 40. otherwise `'the Construction is as shown 'in Figure ,1.

.Figure 6 shows one end of afuse acco'ding ,to ,Figures 1 or 5, wherein the spade bracket 3,! also ,forming-'a terminal, is provided for mountinggthe fuse'and isspot-brazed to the flat end .oran outer `end cap i i i 'In Figura `'7- another .form' of ;Construction is shown in which the star core 5 is support-eclby sleeve terminals 25 extending cutwardly :from the star core `&and having their outer slit ende-*spring over the re-.entrant parts *25 of 'the end :caps .4 and Secured by circlips 41` There is also at each endra packing Washer 23 betweenthe flat end of the 'casing i and the inner flat 'surface of the end cap 4. The outer Caps 22 are, however,' omitted. This fuse isshown 'for stud mounting by-means 'of a 'stud 32 secured in the re-entrant :part 26401? the .left .hand end :cap 4. In this `fuse :it is're- -quired to have a .non-uniform `fusible silver con- =ductor, and as it is difficult to draw a wire of -varying cross-section, the conductorzis 'shown *in Figure'7 "formed of sections of relatively heavy gauge 33 with intermediate sections of finer =gaugea34. These sections are connected in 'series, being oxy-actylene welded together as :indicated at 35. a

Finally, .in Figure B, a fuse according to the invention without a star core is shown; 'Generally speaking, the fuse is 'for stud 'mounting :as in Figure 7, and the end Caps 4 -are arranged similarly. 'There -are two fusible conductors 'in `parallel consisting of sections of heavy' gauge silver wire 33 with intermediate sections 34 'of .finer gauge 'and welded at 35 as in Figure '7.

, 'These conductors, however, are merely 'supported :by the powder filling 20 which'is Shaken into firm contact with theconductors. At either end, 'the conductors are spot welded to terminalthimbles 36 which have their Outer ends split and make a 'push-on fit on the re entrant parts 26 of 'the end'caps 4. Sleeves 31 of ;'polyvinyl chloride 'fit over the thimbles 36 and prevent the refrac- 'tory powder 20 from entering the spaces within 'the thimbles 36. In this construction, 'the thim- -':ble terminals 36 .and the sleeves 37 are'loceted axially by a brass locating Washer 38 at either end gripped between the end of the casing l and the packing washer 23.

In Figures '7 and 8 the fuses are shown without indicators.

I claim:

1. An electrical fuse comprising in combination, a tubular casing of insulating material, a metallic terminal cap closing said casing at each end, said cap having a cylindrical portion telescoping a portion of said casing and providing an intervening annular space, one of said telescoping portions having an annular groove formed in its surface bounding said space, and a yieldable scaling ring compressed between the inner wall of each of said end caps and the outer wall of said casing and retained in said annular groove, and a fusible conductor enclosed in said casing and extending between said end caps, said sealing rings being engaged and deformed under compression by forcing said terminal caps over the body of said casing at both ends, each sealing ring being of sufficient Volume to fill completely the annuiar groove in which it is mounted and to fill a substantial part of said annular space.

2. In 'an electrical fuse, the combination of a tubular casing of insulating material, a metallic terminal cap closing said casing at one end, said cap having a cylindrical portion telescoping a portion of said casing and providing an intervening annular space, one of said telescoping portions having an annular groove formed in its surface bounding said space, and a yieldable sealing ring compressed between the inner wall of said end cap and the outer wall of said casing and retained in said annular groove, and a fusible conductor enclosed in said casing and connected to said end cap, said scaling ring being engaged and deformed under compression by forcing said terminal cap over the end portion of said casing and being of sufiicient Volume to fill completely the annular groove in which it is mounted and to fill a substantial part of said annular space.

3. An electrical fuse comprising in combination, a tubular casing of insulating material, a sheet metal terminal cap tightly fitting over said casing at each end, a hollow star core of insulating material mounted within said casing and supporting a fusible conductor, a tubular plug of yieldable material forced into the bore of said star core at either end and a sheet metal hollow spigot at each end of said casing secured to the respective terminal caps and fitting within said respective tubular plug.

4. An electrical fuse as defined in claim 1, also comprising a pair of fiat scaling rngs each interposed between the flat surface at one end of said casing and the inner fiat surface of said respective terminal cap.

5. An electrical fuse comprising in combination, 'a tubular casing of insulating material, a sheet metal terminal cap tightly fitting over said casing at each end, a hollow star core of insulating material mounted within said casing and supporting a fusible conductor, a tubular plug of yieldable material forced into the bore of said star core at either end, a sheet metal hollow spigot at each end of said casing secured to the respective terminal caps and fitting within said respective tubular plug and a fuse indicator with a slidable plunger and housed in said hollow spigot at one end of said casing.

6. An electrical fuse comprising in combinanation, a tubular casing of insulating material,

a sheet metal terminal cap tightly fitting over said casing -at each end, a hollow star core of insulating material mounted within said casing and supporting a fusible conductor, a tubular plug of yieldable material forced into the bore of said star core at either end, a sheet metal hollow spigot at each end of said casing secured to the respective terminal caps and fitting within said respective tubular plug and a fuse indicator with a slidable plunger and housed in said hollow spigot at one end of said casing, said terminal cap supporting said last-mentioned spigot being formed with a thin perforable wall at its central part adapted to be pierced by the plunger of said indicator on operation of the latter and to retain said plunger in the indicating position.

7. An electrical fuse comprising in combination, a tubular casing of insulating material, a sheet metal terminal cap tightly fitting over said casing at each end and ormed with an inwardly projecting tubular spigot, a hollow star core of insulating material mounted within said casing. a terminal sleeve secured to each end of said star core and projecting outwardly beyond the end of said star core to engage over and to be supported by said spigot of the respective terminal cap and to make electrical contact therewth and at least one fusible conductor supported on said star core and electrically connected at its ends to said respective terminal sleeve.

8. An electrical fuse as defined in claim 7, further comprising a sheet metal indicator housing of tubular form, said housing having an enlarged outer end rendered resilient by slits engaging the inner wall of said inwardly projecting tubular spigot at one end of said casing and making electrical contact therewith.

9. An electrical fuse as defined in claim 7, further comprising a sheet metal indicator housing of tubular form, said housing having an enlarged outer end rendered resilient by slits engaging the inner wall of said inwardly projecting tubular spigot at one end of said casing and making electrical contact therewith, and a fusible conductor housed in said star core and secured at one end to said indicator housing.

10. An electrical fuse as defined in claim 1, further comprising an additional outer end cap at each end fitted over and secured to said respective terminal cap.

11. An electrical fuse as defined in claim 7, further comprising an outer end cap at each end fitted and secured to the respective metal terminal cap.

12. An electrical fuse as defined in claim 1, wherein said fusible conductor mounted within said casing consists of a plurality of conductors of different cross-sectional areas and welded together in series.

13. An electrical fuse as defined in claim 1, and including a star core mounted between said terminal caps, and wherein said fusible conductor mounted within said casing consists of a plurality of conductors of different cross-sectional areas and welded together in series and wound on said star core.

JOHN EDWARD COX.

References Cited in the file of this patent UNITED STATES PATENTS Number 

